Wheeled floor jacks have been in use for many years to raise and lower automobiles. Large capacity models of heavy duty construction and weight have been the mainstay of professional car repair shops and service stations. Smaller, e.g. 1, 11/4, and 11/2 ton capacity floor jacks of lighter weight and construction have been marketed for some time for use by such repair shops for road service and general use. Due to their small size and light weight the general public has adapted them for home use as well and also as a spare jack to be used by the car owner and carried in the trunk of the car.
Examples of such conventional floor jacks are depicted in U.S. Pat. Nos. 4,018,421 and 4,131,263; advertised, for example, in Norco Form 842, 8-77, and in the Key Bar Model 2030 owner manual, both published by Norco Industries, Inc. of Gardena, Calif. Portable floor jacks of a similar nature have been shown on page 91 of Catalog No. 397B of the J. C. Whitney & Co., 1917 Archer Avenue, Chicago, Ill. Numerous other manufacturers and marketers, including those marketed under the Blackhawk trademark, are available.
Such wheeled floor or service jacks, while generally quite useful and popular, do suffer from some drawbacks. A major problem with such jacks results from the requirement that the jack move relative to the load (normally a car) while lifting it. While not a problem on hard surfaces, such as a concrete pad, this is a problem when one attempts to use the jack on a softer or uneven surface such as gravel, hot blacktop surfacing, dirt, snow or sand. Of course, when used as a trunk-carried jack, the jack must be useful on whatever surface the vehicle finds itself.
In typical use, in raising an automobile on such a soft surface, upon taking up some weight of the vehicle, the jack's wheels quickly bite into and sink so that the jack frame rests on the surface. But as it is necessary that the jack frame move relative to the vertical contracting saddle because of the basic design of such jacks, and the automobile is braked and preferably blocked so as not to roll (as per operating instructions of most jack manufacturers), then the frame must "snow plow" into the surface or else the saddle must "slip" relative to the vehicle. Of course, the latter can be harmful to the vehicle and/or the jack and could also cause serious injury to the user if an accidental dropping of the vehicle should occur. Also, when on blacktop surfaces, such as house driveways, the blacktop surface will be permanently "dented" or scarred.
While some have recognized the problem of wheel indenting in other types of jacks and provided a flat platform or base for the jack to spread the weight of the vehicle (e.g. U.S. Pat. Nos. 2,635,715; 2,594,270; 2,563,927; and 2,173,598) such have not been applied to wheeled floor jacks and indeed, if so applied, would result in a dangerous or unworkable jack.
While others have made low-slung lifting jacks for a special purpose (e.g. of car side only--e.g. Blackhawk roadside model 67393-1 ton) and eliminated the wheels, such stationary jacks are of limited use due to the low 1 ton capacity and because of the side only use, it makes it problematic to lift a car alongside a curb. Furthermore, such stationary jacks may be dangerous when used at other than their intended lifting points and for other applications.